notesblognepal.blogspot.com
1. Answer the following questions
a. What is atmosphere? What are the constituent of the
earth atmosphere?notesblognepal.blogspot.com
Answer: It is
the mixture of gases surrounding any celestial object that has gravitational
field strong enough to prevent the gases from escaping. The principal
constituent of the atmosphere are nitrogen and oxygen. There are other gases as
well like carbon dioxide, methane, nitrous oxide and many other gases, which
include both active and inert gases.
b.
What is ozone layer? Where is it found?notesblognepal.blogspot.com
Answer: It is
an atmospheric concentration of ozone found at an altitude of 16-50 k.m above
the earth’s surface. It is tri-atomic structural gas of oxygen atom. It is
found in the stratosphere. [a region of the upper atmosphere, between about
16-50 km in altitude containing a relatively high concentration of ozone that
absorbs solar UV radiation in a wavelength range not screened by other
atmospheric components is called ozone layer. It is also called as
Ozonosphere.]
c.
Mention any four points of importance of ozone layer.notesblognepal.blogspot.com
Answer:
v
In the early history of earth the ozone layer
was absent so there were no terrestrial creatures. Formation of ozone layer
helped in the evolution of terrestrial creatures.
v
It shields the biosphere from the deadly effects
of UV radiation. It is responsible for creating conditions suitable for the
existence of healthy life on the planet. It acts like a protective umbrella for
all living creatures living in the earth.
v
It controls the climate of lower atmosphere. If
there was no ozone layer. The intense heating on this planet would take place.
It would affect the whole climatic pattern and ultimately the environment.
v
The
protective umbrella of ozone protects sun burn, eye irritation, skin cancer and
immune system suppression.
v
Ozone umbrella also protects the aquatic life,
wildlife and crops from being exposed to UV and other harmful radiation.
v
Ozone layer also decreases the acid deposition.
v
It also protects the monuments, out door paints
and plastics. It absorbs the UV rays of the sun and protects the water vapour
from UV dissociation.
d.
What is depletion of ozone layer?notesblognepal.blogspot.com
Answer: The
process of thinning of the ozone by various ozone depleting gases like CO2,
CH4, NO2, CFCs is known as depletion of ozone layer. [An
area of the ozone layer, such as the large area over Antarctica
or the smaller area over the North Pole, that periodically becomes depleted of
ozone is called ozone hole.]
e.
Mention the factors that are responsible for the
depletion of ozone layer?notesblognepal.blogspot.com
Answer: Ozone
can be destroyed by a number of free radical catalysts, the most important of
which are hydroxyl radical, the nitric oxide and atomic chlorine and bromine.
All of these have both natural and manmade sources; at the present time, most
of the OH and NO in the stratosphere is of natural origin, but human activity
has increased the chlorine and bromine, theses elements are found in certain
stable organic compounds, especially CFCs, which may find their way to the
stratosphere without being destroyed in the troposphere due to their low
reactivity. Once in the stratosphere the CL and Br atoms are liberated from the
parent compounds by action of UV light the begin their work of destruction of
ozone layer which can shown in the following chemical reaction:
CFCl3
+ hv→CFCl2 + Cl
Cl+O3→ClO+O2
ClO+O→Cl+O2
f.
Clarify in what way the layer of ozone is depleted due
to the action of CFC products.notesblognepal.blogspot.com
Answer: Ozone
can be destroyed be a number of catalysts, the important of which is CFCs. CFCs
are families on non-reactive, nonflammable gases and volatile liquids. Because
of their properties they are used in a multitude of applications, they are used
in billions of industrial goods each year. The non-reactivity of CFCs, so
desirable to industry, allows them to drift for years in the environment until
they eventually reach the stratosphere. They may find there way to the
stratosphere without being destroyed in the troposphere due to their low
reactivity. High in the stratosphere intense UV solar radiation severs
chlorines off of the CFCs and it is these unattached chlorines that are able to
catalytically convert ozone molecules into oxygen molecules.
Cl+O3→ClO+O2
ClO+O→Cl+O2
g.
“The growing industrialization and modernization have
also been contributing to the depletion of ozone layer”. Do you agree with this
statement? Support your answer giving reason.notesblognepal.blogspot.com
Answer: The
most responsible factor for the depletion of ozone layer is the growing
industrialization and modernization. In the name of modernization people have
invented many devices, technologies and machines which are producing numbers of
ozone depleting gases. If we see the rate of destruction of ozone layer it
started when the world experienced the trend of modernization. Industries are
part of modernization. Industries produce different types of poisonous gases as
a by product and it release them in the atmosphere which is slowly destroying
the chemical structure of the ozone. In the same way industrial development has
developed numbers of dangerous ozone depleting compounds like CFCs, HCFCs, HFCs
and trifluoromethyl sulphur pentafluoride. These gases are responsible in the
destruction of ozone layer. On the other hand unmanaged industrialization and
the urge of modernization had destroyed millions of acres of valuable forest.
Decrease in the area of forest and vegetation has increased the percentage of
CO2 in the atmosphere and which is also creating ozone layer
depletion.
h.
Mention any four
impacts of ozone layer depletion.notesblognepal.blogspot.com
Answer: We
know that ozone is a protective layer of the earth. Its depletion causes fatal
diseases like cancer. Some major impacts of ozone layer depletion are detailed
in brief below.
Health hazard: The penetration of high
energy ultra violet rays cause the skin cancer, skin burn, snow blindness,
leukemia, heart diseases and damage the immune system. DNA damage leads to
diseases like mutation, melanoma and leismania.
Loss of aquatic life: Planktons and
microscopic organisms are most vulnerable to UV rays. These organisms play
vital role in aquatic food chain of both fresh water and marine habitat, this
depletion of ozone layer may lead to lass of life from the respective habitats.
Due to the entrance of UV rays average temperature of earth is increased.
Consequently it leads to the increase in water temperature of aquatic habitat.
Different stages of life cycle of aquatic fauna will be affected. The aquatic
ecosystem will be misbalanced due to the destruction of ecological food chain.
Loss of terrestrial life: UV rays
adversely affect terrestrial life too. Especially lower animals and plants that
are found in equatorial region are highly affected. As they are the base of the
ecosystem, the depletion of ozone layer affects their life activities and
disturbs the entire ecosystem.
Crop production: The over exposure of
UV rays destroy the protein content of plants, deplete the chlorophyll content
and leads to the decrease of the photosynthesis activity and crop production.
Climatic Change: The depletion in ozone
layer may lead to the entrance of solar radiation directly to the earth
surface. The heat accumulated in earth changes the climatic pattern and causes
global warming. Due to excess of heat, the rate of evaporation of eater from
water sources will be higher. It causes heavy rainfall in some places and
drought in other places. The polar ice
starts to melt which results into flooding. It consequently raises the sea
level, the costal settlement will be submerged under water and life and
property will be highly affected.
i.
How does the depletion of ozone layer affect an
ecosystem also?notesblognepal.blogspot.com
Answer: Eco-system
is a complex form composed of living and non-living beings. They are
interdependent with each other. Their existence is affected by the existence of
each other. Their condition is determined by the environmental situation. When
the ozone layer depletion occur it directly affect in the various living
organism. It becomes threat for many living creatures. Photosynthesis process
in the plants can not occur, protein present in the leaves get destroyed, it
affects the fertility capacity of living creatures, global temperature
increases and created difficulty in living. Many plant friendly bacteria may
cease to exist; these and other various catastrophes that may fall on the lives
of living being may disrupt the natural ecosystem. Not only are this, various
natural cycle also affected by ozone layer depletion which in turn may be
responsible for affecting the ecosystem.
j.
“Efforts made at the global level may be more effective
for the conservation of ozone layer”. Clarify the statement.notesblognepal.blogspot.com
Answer: Ozone
layer depletion is global problem. Destruction of ozone layer has not occurred
only because of single nation. It is a problem created by human civilization so
there should be the attempt of all global community. The nature of gaseous
wastes is not like that of solid wastes, remaining in a certain place as a
problem. A pollution created in one nation affects the other nation. Effort of
a single nation may not become so fruitful; it may become just like in a
community of 20 families 15 trying to clean the community and the 5 families
are neglecting cleanliness. If the 5 families do not do co-operation in the
program the whole effort becomes failure. The same thing implies for the world.
If we make a joint effort, we can become economically, technically,
environmentally strong to conserve the ozone layer. We can share our knowledge
and experience with each other. We can make a joint commitment for the
protection of the ozone layer. We all know unity has strength.
2. Write short note on:notesblognepal.blogspot.com
- Ozone:
Answer: Ozone
is tri-atomic oxygen that exists in the Earth’s atmosphere as a gas. Ozone is
highest in stratosphere at an altitude of 19-48 kilometers above the earth
surface. It is a colourless gas soluble in alkalis and cold water; a strong
oxidizing agent, highly poisonous gas with a strong odour. It is deep blue and
strongly magnetic. Ozone in the lower atmosphere is an air pollutant with
harmful effects on the respiratory systems of and will burn sensitive plants;
however, the ozone layer in the upper atmosphere is beneficial. It is made up
of three atoms of oxygen. It is an allotrope of oxygen that is much less stable
than the diatomic allotrope. It is produced when electric spark is passed
through oxygen or by the action of UV radiation in the stratosphere. Its
process of formation in the presence of UV in the stratosphere is given below.
O2+hv→O+O
O2+O→O3
- Ozone hole: -notesblognepal.blogspot.com
Answer: The
Antarctic ozone hole is an area of the Antarctic stratosphere in which the
recent ozone levels have dropped to as low as 33% of the pre-1975 values. The
ozone hole occurs during the Antarctic spring, from September to early December
as, strong westerly winds start to circulate around the continent and create an
atmospheric container. Within this “polar vortex”, over 50% of the lower stratospheric
ozone is destroyed during the Antarctic spring. The overall cause of the ozone
depletion is the presence of chlorine-containing source gases. In the presence
of UV light, these gases dissociate, releasing chlorine atoms, which then go on
to catalyze ozone destruction. The Cl-catalyzed ozone depletion can take place
in the gas phase, but it is dramatically enhanced in the presence of polar
stratospheric cloud (PSCs)
- Stratosphere:
Answer: the
layer of atmosphere above troposphere is called stratosphere. It is extended
from 16 km to 50 km above the earth surface. Its thickness is about 34 km. this
region is also called Ozonosphere because its major component is Ozone. Other
components of stratosphere are N2, O2 and nascent Oxygen.
Ozone is a special type of oxygen containing three oxygen atoms. The layer of
ozone protects us from the harmful effects of UV rays of the sun. The
absorption of solar radiation heats the upper layer of stratosphere. In this
layer temperature varies from -550 Celsius to -20
Celsius. The upper boundary of stratosphere is Stratopause, which has the
temperature of 20 Celsius. This layer may have the cloud Cirrus at
the lower level. This layer is clear and cloudless, that’s why jet planes often
fly in this layer.
- Ultraviolet radiationnotesblognepal.blogspot.com
Answer: Electromagnetic
radiation having wavelength between that of violet light and long X-rays, i.e.
between 400 nanometers and 4nm. In the range 400-300 it is known as the near
ultra violet. In the range 300-200 nm it is known as the far ultraviolet, and
below 200 nm is known as extreme ultraviolet or the vacuum ultraviolet. The sun
is strong emitter of the UV radiation but only the near UV reaches the surface
of earth as the ozone of the atmosphere absorbs all wave length below 290 nm.
UV radiation is classified in three ranges according to its effects on the
skin.
UV-A
(320-400nm) is not harmful in normal doses and used clinically in the treatment
of certain skin complaints.
UV-B
(290-320nm) causes reddening of the skin followed by the pigmentation and
excessive exposure can cause severe blistering.
UV-C (230-290
nm) causes skin cancer. These days probabilities of UV radiation have increased
because of ozone layer depletion.
- Ozonospherenotesblognepal.blogspot.com
Answer:
Atmospheric concentration of ozone found at an altitude of 10-50 Km above the
Earth’s surface. In this layer most of the sun’s UV radiation is absorbed by
the ozone molecules. By absorbing most of the solar UV radiation the ozone
layer protects living organism on earth. The fact that the ozone layer is the thinnest
at the equator is believed to account for the high equatorial incidence of skin
cancer as a result of exposure to unabsorbed solar UV radiation. In 1980s it
was found that depletion of the zoomed layer was occurring over both poles,
creating ozone holes, this is thought to have been caused by a series of
complex photochemical reaction involving nitrogen oxides and halons. CFCs rise
to the stratosphere, where they react with UV light to release chlorine atoms;
these atoms, which are highly reactive catalyze the destruction of ozone.
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